1. Field of the Invention
Present invention relates to limit switches and particularly to such switches mounted in explosion proof housings for providing limit indications of the positions of rotary driven control devices such as rotary valves.
2. Description of the Prior Art
Small sensitive switches are in common use today for electronic and electro mechanical equipment as interlocks and position sensors. In most usages, there are no particular requirements for reducing hazards of flame, explosion or corrosion. However, in a number of rotary control devices, such as for example rotary valves, operation in the presence of acids and or alkalines is fairly common as well as operation with explosive and inflammable gases and liquids. In these same situations, it is frequently a necessity or at least a high desirability to be able to know the position of the control device or to interlock the position of a control device with some other device or indicator.
Limit switches that are sealed for protection against one of the above conditions have been built into a rotary control device as an inherent part of the device. They have also been mounted on the end of a rotary control shaft of a control device. Generally the limit switches mounted on the end of a control shaft prevent manual override operation of the control shaft. Limit switches built into a control device require disassembly of the device for any maintenance of the switch. Installation and removal of explosion-proof limit switches are cumbersome with difficultly in adjustment.